Action Points

Note that this study suggests that psoriasis is an independent risk factor for the development of type 2 diabetes mellitus.

Note also that the risk occurred in a dose-dependent fashion and that patients with severe psoriasis who develop diabetes mellitus are more likely to receive systemic therapy in comparison with patients with diabetes mellitus but without psoriasis.

Incident diabetes was a modest but significant 14% more likely among individuals with the skin disease after adjusting for a range of other factors, Rahat S. Azfar, MD, of the University of Pennsylvania in Philadelphia, and colleagues found.

Severe psoriasis raised the risk most -- with a hazard ratio of 1.46 (95% CI 1.30 to 1.65) -- but the risk was also statistically significant among mild cases, the group reported online in the Archives of Dermatology.

Extrapolating these numbers to the roughly 125 million psoriasis cases worldwide, the risk the condition poses may add 115,500 people each year to the type 2 diabetes ranks.

"These findings, combined with the large literature linking psoriasis to cardiovascular and metabolic disease, suggest that patients with psoriasis should be encouraged to lower their risk of diabetes mellitus and its complications by undergoing therapeutic lifestyle changes and appropriate screenings for signs of insulin resistance," the researchers recommended.

Links to myocardial infarction, stroke, metabolic syndrome, and cardiovascular mortality found in prior studies are thought to be due to the chronic inflammation of psoriasis.

The same may be true for the link to diabetes, as the inflammatory cytokines that drive psoriasis also promote insulin resistance and metabolic problems, Azfar's group suggested.

They looked for an association in The Health Improvement Network (THIN), an electronic medical records database of general practices covering a representative 5% of the British population.

The study included 108,132 adults with psoriasis and 430,716 patients without psoriasis, matched for where and when seen for an office visit.

The relationship between incident diabetes and psoriasis appeared to be "dose"-dependent.

The hazard ratio was 1.14 (95% CI 1.10 to 1.18) with mild psoriasis and 1.46 (95% CI 1.30 to 1.65) with severe psoriasis after adjustment for age, sex, body mass index, hypertension, and high cholesterol.

That meant an extra 0.9 cases of type 2 diabetes could be attributed to psoriasis annually per 1,000 patients with the skin condition overall, or 0.7 cases among those with mild psoriasis and three cases in severe psoriasis.

When looking just at the patients who developed diabetes in a nested study, patients with mild psoriasis weren't more likely to be treated with diabetes medications than those who had no psoriasis.

But severe psoriasis predicted 53% higher chances of getting an oral hypoglycemic agent for incident diabetes with a nonsignificant trend for greater likelihood of a prescription for insulin as well (odds ratio 1.32, 95% CI 0.75 to 2.33).

Why patients with severe psoriasis were more likely to be prescribed such medications isn't clear, and further research is needed, Azfar's group noted.

The overall diabetes risk and treatment findings were robust to sensitivity analyses excluding psoriatic arthritis patients, those without at least annual clinic visits, and such.

But the researchers noted that their observational findings may have been limited by some misclassification of psoriasis because of using treatment patterns to determine severity and could not entirely exclude possible information bias or confounding from unmeasured or unknown factors.

The observational study design also meant causality couldn't be determined.

The study was supported by a National Institute for Arthritis and Musculoskeletal and Skin Diseases grant, a National Heart, Lung, and Blood Institute grants, and a University of Pennsylvania dermatology departmental training grant.

Azfar reported having no conflicts of interest to disclose.

One co-author reported being on the data safety monitoring boards for Abbott, Astellas, and Centocor. Another reported receiving grants from Amgen, Pfizer, Novartis, and Abbott and consulting for Amgen, Abbott, Pfizer, Novartis, Celgene, and Centocor.

Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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